I. Field of the Invention
The invention is directed generally to the field of digital information systems and, more particularly, to a bus interface controller apparatus for use in computer graphics systems.
II. Discussion of the Prior Art
Many graphics, communications, and DSP applications require a large amount of information processing, most of which is passed through some form of high speed memory. Manufacturers of such memory devices have made dramatic improvements in the areas of speed and density over the past few years. In applications that require multiple bus access into and out of such dense high speed memory products, an increasingly high portion of the surface area available on a printed circuit board and an increasingly higher percentage of the available bandwidth of a typical system is being consumed by the semi-conductor devices which interface with such memory devices. The invention provides a design for use as a memory interface which reduces the number of parts required in many applications and can be universally adapted to many applications.
Some examples of known memory interface chips include the 373/374 latch or 244/245 buffer/transceiver. Texas Instruments, Inc. has produced a crossbar switch Model No. 74AS8840 which includes 64 I/O pins arranged in 16 4-bit groups, where each group of four pins serves as a bi-directional input to an output from a 4-bit multiplexer. Also available are devices such as AMD Company's Model No. Am29C98 which is a 9-bit by four port multiple bus exchange device. Typical port-to-port delays for such devices are in the 9 to 10 nanosecond range. Such devices also require a large amount of external user-supplied control logic relative to the interface device of the invention. Speeds in the 9 to 10 nanosecond range are too slow for many current applications requiring high speed processing, such as graphic display systems. The invention has advantages over the known devices of the prior art including internal latching buffering architecture which is user configurable, via output configuration control lines. Through the use of the gallium arsenide (GaAs) technology for fabrication of the design, the invention provides the speed necessary with TTL/CMOS compatible inputs and outputs.